2,3-Diamino-5,6-dihalopyrazines, in which halo is Br, Cl or F, are intermediates for the preparation of herbicides and antimicrobials. U.S. Pat. No. 3,822,261 discloses the preparation of herbicidal imidazopyrazines such as ##SPC1##
From the corresponding pyrazine compounds ##SPC2##
X being Br, Cl or F. U.S. Pat. No. 3,850,929 similarly discloses the preparation of microbicidal thiadiazolopyrazines of the structure ##SPC3##
In which X and Y are Br or Cl.
The 2,3-diamino-5,6-dihalopyrazine intermediates utilized in the preceding patents can be prepared by reacting corresponding tetrahalopyrazines with ammonium hydroxide, according to the procedure of G. Palamidessi and F. Luini, Farmaco. Gd. Sci., 21, 811 (1966); Chemical Abstracts, 66, 37886g (1967). However, the 2,6-diamino-dihalo isomers are co-produced with the desired intermediates (except when tetrafluoropyrazine is the starting material). Palamidessi and Luini disclose no method of separating the isomers, as such, from each other and ordinary separatory procedures, such as fractional crystallization are generally not effective for this purpose. In those instances where the mixed isomers cannot be employed as such (as by selective reaction or conversion to more readily separated isomeric products), a convenient method of separation is highly desirable.